In mobile networks, e.g., according to the Third Generation Partnership Project (3GPP), a control channel may be used to convey control information to a user equipment (UE). An example of such a control channel is the Physical Downlink Control Channel (PDCCH) as specified for 3GPP LTE (Long Term Evolution). The PDCCH is transmitted in the L1/L2 control region of a subframe. The L1/L2 control region is composed of the first, up to four, Orthogonal Frequency Division Multiplexing (OFDM) symbols of the subframe and spans the entire frequency domain.
Relaying was introduced in LTE Release 10. Since a relay node (RN) might not be able to receive the regular control channel, i.e., the PDCCH, from its donor base station (BS), in 3GPP LTE referred to as Donor eNB (DeNB), a further control channel, referred to as Relay PDCCH (R-PDCCH), was introduced. The R-PDCCH is not transmitted in the L1/L2 control region. Instead, the R-PDCCH is transmitted in the regular data region of a subframe. In the time domain, a subframe is divided into a first slot and a second slot. In the first slot, the R-PDCCH starts at the fourth OFDM symbol of the slot and ends at the end of the slot. In the second slot the R-PDCCH starts at the first OFDM symbol of the slot and ends at the end of the slot. In the frequency domain the R-PDCCH is transmitted on one or more resource blocks (RBs). Downlink (DL) assignments are transmitted on an R-PDCCH in the first slot and uplink (UL) grants are transmitted on an R-PDCCH in the second slot.
Coding, scrambling and modulation for the R-PDCCH follow the same principles as for the PDCCH. However, the mapping of the R-PDCCH to time-frequency resources is different. In a variant of the R-PDCCH which is based on UE specific Demodulation Reference Symbols (DMRS), there is no cross-interleaving of multiple R-PDCCHs in a single RB. Rather, one R-PDCCH is mapped to one set of RBs, the number of RBs, which may be 1, 2, 4 or 8, depending on the aggregation level. An example of such R-PDCCH transmission is shown in FIG. 1. Without cross-interleaving, the R-PDCCH can be transmitted on antenna ports with UE-specific DMRS.
For the R-PDCCH, DL assignments are transmitted in the first slot of a subframe and UL grants are transmitted in the second slot of a subframe. Transmitting DL assignments in the first slot and UL grants in the second slot of a subframe forces a receiver to receive during the entire subframe. Hence such a design prevents a concept referred to as micro sleep, where the receiver can power down some of its components after it has detected that there is no DL assignment in a particular subframe. Further, separating DL assignments and UL grants to be transmitted in two different slots requires one blind decoding attempt in each slot space, one for the DL assignments, transmitted with Downlink Control Information (DCI) format 1A, and one for the UL grants, transmitted with DCI format 0. Hence, it increases the total number of blind decoding attempts.
Accordingly, there is a need for techniques which allow for efficiently transmitting control information to a receiving node.